Sheet stacking apparatus and image forming apparatus

Abstract

A sheet stacking apparatus has a stack tray which can move so that a sheet stack surface keeps a constant position from a discharge outlet and which is a finisher capable of using the stack tray by switching it. When stacking the maximum number of sheets to be stacked on the stack tray and preventing stacking of sheets on the stack tray up to the maximum number of sheets to be stacked and the number of sheets stacked on the stack tray reaches a predetermined number of sheets to be stacked which does not prevent up to the maximum number of sheets from being stacked on the stack tray, stacking of sheets on the stack tray is temporarily prohibited to stack sheets by switching to the stack tray. Thereby, all sheet stack trays can stack up to the maximum number of sheets to be stacked, decrease of the number of stacked sheets is prevented in the whole sheet stacking apparatus and the number of temporal interruptions of a job is decreased.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a sheet stacking apparatus for stacking sheets output from an image forming apparatus such as a copying machine, printer or facsimile, particularly to a sheet stacking apparatus so that all stack trays can stack the maximum number of sheets to be stacked to prevent the number of sheets to be stacked of the whole apparatus and decrease the number of temporary interrupt times of jobs and an image forming apparatus having the sheet stacking apparatus.

[0003] 2. Related Background Art

[0004] A sheet processing apparatus as a sheet stacking apparatus is conventionally proposed which successively conveys sheets in which an image is recorded by an image forming apparatus into the sheet processing apparatus and selectively applies predetermined processing such as punch processing, stapling or sorting. Some of the sheet processing apparatus respectively have a plurality of sheet stack trays (...

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